<!DOCTYPE html>
<html lang="zh-CN">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    html {
      width: 100vw;
      height: 100vh;
      /*
        linear-gradient([方向], ...颜色)
        方向
         ● to 方位名词
         ● 度数，单位：deg
       */
      /* background-image: linear-gradient(red, orange, yellow); */

      /* to 方位名词 */
      /* background-image: linear-gradient(to bottom right, red, orange, yellow); */

      /* 度数 */
      background-image: linear-gradient(45deg, red, orange, yellow);
    }
  </style>
</head>

<body>
</body>

</html>